The abrasives industry generally concerns abrasive products comprising a binder and a plurality of abrasive grains. During abrasion, the abrasive grains are brought into contact with a work surface generally at a considerable pressure and with development of a substantial amount of heat. It is important for such operations that the abrasive products appropriately retain the abrasive grains. That is, generally, premature release of the abrasive grains from the abrasive products is to be avoided.
A variety of abrasive products are known, including coated abrasive products, bonded abrasives and nonwoven abrasives. In general, coated abrasive products comprise a substrate or backing having a layer of abrasive grains secured thereto by means of adhesive or binder. A bonded abrasive generally comprises a solid mass formed from abrasive grains and binder, for example a grinding wheel or a cutoff wheel. Nonwoven abrasives generally comprise abrasive grains bound onto and in a nonwoven fibrous substrate by means of binder or adhesive.
Generally, premature release of abrasive grains has been a problem with respect to all of the various types of abrasive products even those from which a controlled rate of release is desired. The problem is particularly significant when the abrasive product is used for high stock removal applications. During such uses, the abrasive product must be able to withstand high pressures and rotative speeds, while still providing a good, sufficient abrasive cut. For example, a coated abrasive disk may traverse 12,000 revolutions per minute (rpm) and be subjected to an interface pressure as high as 15 kg/cm.sup.2. Such severe conditions may be preferred for certain applications as they result in increased cut rates. However, they severely tax the integrity of the bond between the abrasive grain and the binder (adhesive) system. If the bond at this interface fails, the abrasive grains are rejected (or shelled) from the abrasive product.
In the coated abrasive industry, the term "shelling" is sometimes utilized to refer to the phenomenon of abrasive grain release from binder, in use. Generally, the term "shelling" is applied whether the product involved is a coated abrasive or some other form of abrasive product, such as a bonded abrasive or nonwoven abrasive. Herein, the term "shelling" is meant to refer in general to premature (i.e. undesired) release of abrasive grains from a binder system (or bond system) without regard to type of construction or substrate involved.
It has been recognized that improvement of the bond between the abrasive grains and the binder system will occur if the surfaces of the abrasive grains are rough rather than smooth. Thus, early efforts to improve the performance of abrasive products with respect to shelling focused on creating a rough surface on the abrasive grains, to facilitate adherence. In more recent years this has evolved into the application of material to the surface of the abrasive grains, which provides a rough surface to facilitate engagement with the adhesive.
In addition, the performance of an abrasive product will in part reflect the characteristics of the abrasive particles. If the abrasive particles are very hard, but not sufficiently tough, they will have a propensity to crack, fracture or crush in use, due to brittleness. The effect of such a failure is analogous to that of premature shelling, i.e. premature loss of an abrasive grain from securement in a useful and operational manner in an abrasive product. A variety of methods have been utilized to improve the performance of abrasive grains with respect to this. These have greatly concerned the chemical and physical nature of the abrasive grains including its composition, density, structure, crystalline nature, etc.